The present invention relates to a control unit for an oil hydraulic circuit through which lubricating oil flows, such as is used in automobile engines and the like. In particular, the invention relates to a control unit for a hydraulic circuit, which, while the vehicle engine is running, allows the lubricating oil flowing in the circuit to be supplied and removed in a manner that will keep the oil at a certain level, and also allows different types of lubricating oil to be supplied to prevent fuel from diluting the lubricating oil.
Engines, such as automobile engines, include many metallic parts, such as pistons, cylinders, crankshafts, connecting rods, and bearings which slide against one another or rotate. For this reason, a lubricating apparatus is provided for the engine to supply lubricating oil to these metallic parts.
In such a lubricating apparatus, the lubricating oil is collected in an oil pan and is pumped therefrom by an oil pump. After passing through an oil filter which removes foreign matter and an oil pressure regulator which regulates oil pressure, the lubricating oil is transferred by pressure to each of the sliding portions of the engine and returned to the oil pan.
In a wet sump type lubricating apparatus, which has an oil pan mounted directly to the bottom of the engine cylinder block, the lubricating oil is pumped up from an oil suction mouth and ejected onto each of the sliding portions. The oil is then allowed to fall naturally and is returned to the oil pan. In this type of apparatus, the oil pan serves not only as an oil tank which has the necessary capacity for oil circulation, but also as an oil cooler because the bottom of the oil pan is exposed at the lower surface of the car body.
In high performance cars such as racing cars which move rapidly at high speeds, a large acceleration is frequently exerted longitudinally and laterally on the moving car. Therefore, in the wet sump lubricating apparatus which contains collected lubricating oil in the oil pan, the suction mouth may be exposed above the oil surface and suck air, so that the engine may run out of oil. To solve this problem, a dry sump type lubricating apparatus is used. In the dry sump lubricating apparatus, an oil tank which contains collected lubricating oil is separately provided, in addition to an oil recovery sump. The sump is located in the crankcase to recover oil which has been ejected onto the sliding portions of the engine. In addition, a recovery pump, provided in addition to a booster pump, is used to return the lubricating oil from the oil recovery sump to the oil tank.
However, in the above-described wet sump type lubricating apparatus and the dry sump type lubricating apparatus, when the amount of oil in the hydraulic circuit decreases, there is not enough lubricating oil to eject onto the lubricating portions of the engine, so that a suitable oil film cannot be maintained, often resulting in abnormal wear or seizure of the sliding parts. In contrast to this, when there is too much oil in the circuit, excess oil is also supplied to the cylinder and the like, so that the oil may spatter onto the spark plugs to give rise to ignition failure. Accordingly, the oil which circulates through the hydraulic circuit must be kept at the correct level.
In a conventional lubricating apparatus, when the amount of oil decreases by, for example, consumption, it is necessary to stop the car and supply lubricating oil by hand. In particular, when the car moves at a high speed of approximately 160 km/hr, more lubricating oil is consumed as compared to when the car moves at a normal speed of approximately 60 km/hr. Accordingly, cars having a conventional lubricating apparatus cannot be driven at a high speed for a long period of time.
When there is too much circulating lubricating oil, which is caused by supplying too much oil, it is necessary to remove the drain plug by hand from the lubricating apparatus to remove the oil.
In the lubricating apparatus having an oil cooler, when the temperature of the lubricating oil rises, a thermostat operates to divert the oil from the oil circulation path to a bypass which contains an oil cooler. This results in an increase in the total amount of oil needed for circulation, the added increment being equivalent to the capacity of the oil cooler bypass. Consequently, the oil surface of the oil tank rises, often causing ignition failure due to spattering of oil onto the spark plugs. When the oil is diverted to the oil cooler bypass, the oil level of the oil tank is changed. The larger the capacity of the oil cooler, the greater the change in the oil level. Therefore, when installing an air-cooled or oil-cooled engine having a displacement of more than 5000 cc in the car, the cooling capacity of the oil cooler must be increased with the increased displacement of the engine. This results in a greater change in the oil level in the oil tank, which makes it difficult, if not impossible, to use an engine having a high displacement.
On the other hand, for example, as one drives at a speed of approximately 60 km/hr through hot cities, the oil temperature increases, which causes a thermostat to begin cooling the oil by means of the oil cooler. However, when one drives away from such cities and enters highways such as autobahns, driving at a high speed of approximately 210 km/hr in a cool region for a long period of time, the oil will be cooled by the ambient air temperature. In such cases, the thermostat will operate to stop the oil from flowing to the bypass containing the oil cooler. This reduces the total amount of circulating oil, and, in addition, increases the amount of oil consumed due to high-speed driving. This may result in worn and seized sliding parts.
In addition, the lubricating oil expands and contracts with temperature changes. This means that there is a difference in the oil level of the oil tank immediately after the car is started as compared to when it has been driven at a high speed.
Further, since the lubricating oil is also ejected in the cylinder, fuels such as gasoline are mixed in the collected lubricating oil. This dilution with fuel reduces the viscosity of the lubricating oil and makes it impossible to maintain a suitable oil film. This can lead to several engine problems. For example, when one drives at approximately 160 km/hr for about 24 hours, the fuel dilution rate is said to be about 15%. The only thing which can be done to overcome this problem of dilution with fuel is to increase the initial viscosity of the lubricating oil. Increasing the viscosity, however, increases the mixture resistance of the lubricating oil and leads to losses in engine output.